Supermoon
A supermoon is the coincidence of a full moon or a new moon with the closest approach the Moon makes to the Earth on its elliptical orbit, resulting in the largest apparent size of the lunar disk as seen from Earth. The technical name is the perigee-syzygy of the Earth-Moon-Sun system. The term "supermoon" is not astronomical, but originated in modern astrology.Kryptonite for the supermoon | Bad Astronomy | Discover Magazine The association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events such as earthquakes and volcanic eruptions, but the evidence of such a link is widely held to be unconvincing."No Link Between 'Super Moon' and Earthquakes" at news.discovery.com The most recent occurrence was on September 9, 2014. The opposite phenomenon, an apogee-syzygy, has been called a micromoon,http://earthsky.org/tonight/micro-moon-years-smallest-full-moon-on-january-15-16 though this term is not as widespread as supermoon. Distance The Moon's distance varies each month between approximately and due to its elliptical orbit around the Earth (distances given are center-to-center). According to NASA, a full moon at perigee is up to 14% larger (in area, or almost 7% larger diameter) and 30% brighter than one at its farthest point, or apogee. Terminology The name SuperMoon was coined by astrologer Richard Nolle in 1979, arbitrarily defined as: }} Nolle also claimed that the moon causes "geophysical stress" during the time of a supermoon. Nolle never outlined why the 90% was chosen. The term supermoon is not used within the astronomical community, which use the term perigee-syzygy or perigee full/new moon. Perigee is the point at which the Moon is closest in its orbit to the Earth, and syzygy is when the Earth, the Moon and the Sun are aligned, which happens at every full or new moon. Hence, a supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time. Frequency The full moon cycle is the period between alignments of the lunar perigee with the sun and the earth, which is about 13.9443 synodic months (about 411.8 days). Thus approximately every 14th full moon will be a supermoon. However, halfway through the cycle the full moon will be close to apogee, and the new moons immediately before and after can be supermoons. Thus there may be as many as three supermoons per full moon cycle. Since 13.9443 differs from 14 by very close to , the supermoons themselves will vary with a period of about 18 full moon cycles (about 251 synodic months or 20.3 years). Thus for about a decade the largest supermoons will be full, and for the next decade the largest supermoons will be new. Effect on tides The combined effect of the Sun and Moon on the Earth's oceans, the tide, is greatest when the Moon is either new or full. At lunar perigee the tidal force is somewhat stronger, resulting in perigean spring tides. But even at its most powerful this force is still relatively weak causing tidal differences of inches at most. As the tidal force follows an inverse-cube law, that force is 19% greater than average. However, because the actual amplitude of tides varies around the world, this may not translate into a direct effect. It has been claimed that the supermoon of March 19, 2011 was responsible for the grounding of five ships in the Solent in the UK, but such claims are not supported by any evidence. Natural disasters There has been speculation that natural disasters, such as the 2011 Tōhoku earthquake and tsunami and the 2004 Indian Ocean earthquake and tsunami, are causally linked with the 1-2 week period surrounding a supermoon. No evidence has been found of any correlation between supermoons with major earthquakes. Gallery File:Supermoon over Germany, 2011.jpg|Supermoon over Münster, Germany, March 19, 2011 Image:Photograph of the Supermoon at Umaid Bhavan Palace, Jodhpur.jpg|Supermoon of June 23, 2013 at Umaid Bhawan Palace, India File:Phases_2014_fancy_1080p30.oggtheora.ogv|The geometry of the Moon's orbit in motion during 2014 References External links * Photo comparing full moon at 222,000 miles with one at 248,000 miles *Richard Nolle's definition * . * CBC News, Gallery of the March 19, 2011 supermoon, viewed from across Canada (Dead link as of 2014.08.11) * BBC News, Gallery of shared pictures Category:Astrology Category:Astronomical events Category:Lunar science Category:Moon